Now some testing I did, showing how VLB advanced graphics performance on 486 computers.
Computer:
486-DX2 66
Asus VL/I-486SVGO VLB board
32meg RAM
240gb hard drive
Winbond VLB I/O controller card
Intel etherexpress 10mbit ISA ethernet
Using a series of graphics cards, from low end ISA to medium end VLB I have done some benchmarks.
3dBench DOS Benchmark:
15.1 fps - Trident 9000i ISA card
30.4 fps - Tseng ET4000 ISA (at 8.25mhz ISA bus)
31.8 fps - Tseng ET4000 ISA (at 11mhz ISA bus, causes artifacts in windows)
48.5 fps - Tseng ET4000 VLB
46.8 fps - Cirrus Logic GD5428 VLB
50.1 fps - S3 804 VLB
Doom max settings (lower ticks are better)
8001 ticks - Trident 9000i ISA
4743 ticks - Tseng ET4000 ISA (at 8.25mhz ISA bus)
4601 ticks - Tseng ET4000 ISA (at 11mhz ISA bus, causes artifacts in windows)
2609 ticks - Tseng ET4000 VLB
2691 ticks - Cirrus Logic GD5428 VLB
2567 ticks - S3 804 VLB
Windows performance - Wintach (at 800 x 600 resolution in 8bit colour)
4.37 times reference - Trident 9000i ISA
12.33 times reference - Tseng ET4000 ISA (at 8.25mhz ISA bus)
12.79 times reference - Tseng ET4000 ISA (at 11mhz ISA bus, causes artifacts in windows)
19.80 times reference - Tseng ET4000 VLB
28.94 times reference - Cirrus Logic GD5428 VLB
31.24 times reference - S3 804 VLB
In subjective terms playing doom on default settings
Trident 9000i - Its possible to play, but you would have to be really desperate because it is a slideshow.
ET4000 ISA - More playable, still rather choppy, If this was the computer I had in the day, I'd play doom this way I guess.
VLB cards - Quite smooth, not perfect FPS but pretty close. Definitely noticeably better than the ISA cards.
I'd definitely recommend avoiding ISA video cards for a 486 class computer.